Ceramic filtering media of ceramic carbide and a process for making same are known, for example, from the German Patent 33 05 529. Such filter bodies can, because of their chemical stability and their to high temperatures and to temperature resistance fluctuation be used as hot gas filters, through-flow electrodes or catalyst carriers.
For these and also for other applications it is, however, advantageous for such fluid-permeable silicon carbide bodies to be electrically heatable with low voltages, especially voltages below 50 volts, so that they can serve both as filters and simultaneously as heating elements.
For this purpose, a silicon carbide body has been provided, for example, in German Patent 33 05 529 with a high electrical resistance of 20 k.OMEGA.cm for use as a heating element. It is indeed also known that the electrical conductivity of silicon carbide can be varied over a wide range by suitable doping with aluminum, boron, nitrogen, etc.
Thus silicon carbide structural elements are doped with nitrogen by annealing them in a nitrogen atmosphere at 1900.degree. C. for several hours. This is, however, an especially slow process and, in any event, the electrical resistance of such doped silicon carbide bodies is always too high for the use of such bodies as heating elements in the low voltage range.